Photothermographic composition



Patented Oct. 9, 1934 UNITED STATES PATENT OFFICE Rochester, N. Company,New York Y,, assignors to Eastman Kodak Rochester, N. Y., a. corporationof No Drawing. Application December 11,, 1930,

Serial No. 501,663

10 Claims.

This invention relates to photo sensitive compositions and photographiclayers and their use for producing images in various photographicprocesses.

It has been found that the thermal decomposition of various substancesis catalyzed by nuclei of one kind or another. We have found a methodwhereby these substances which may be decomposed by heat can beinnoculated with nuclei by exposure to light, whereupon the thermaldecomposition ensues more readily because of the presence of suchnuclei. The action of heat upon such a substance may then be used as thebasis of a process for the formation of an image, which may either be avisible image as ordinarily produced by photographic processes, a reliefimage, or an image which is distinguished from the background in that itdiffers in details of structure, such as granularity or surface texture.

Materials which are useful for our purpose are those substances which wedescribe as photothermographic. These substances are all afiected bylight. Under the action of light there are produced on the molecules ormolecular aggregates nuclei of a new solid phase. The presence of thesenuclei is, of course, not visible to the eye nor is it usually visiblemicroscopically. Ex-

posure below a certain value produces no visible eiiect. In some caseseven prolonged exposure produces no visible image. On subsequentexposure to heat the thermal decomposition of the original solid iscatalyzed by these nuclei. The decomposition will normally be initiatedat the boundary of such a nucleus and the surrounding materialconstituting the molecule or molecular aggregate, and will rapidlyproceed outward from this point. The product of this decomposition willusually be a new solid phase such as metal, metal oxide, metal sulfide,or the like, or it may be a gaseous or volatile substance, such ascarbon dioxide, carbon monoxide, oxygen, or nitrogen, or products ofboth kinds. Photothermographic substances are therefore chemicalcompounds of a definite type in which thermal decomposition of thecompound is catalyzed by previous illumination to light' It isunderstood, of course, that other forms of radiant energy than visiblelight may be used, such as ultra-violet radiation or X-rays.

Photothermographic substances having the properties just described willusually fall in the class of so-cailed heavy metal compounds, that is,salts and compounds of metals other than the alkali and alkaline earthmetals. Salts which are particularly useful in the application of ourinvention will be those in which the anion is capable of decompositionto form one of the gases mentioned, such as carbon monoxide, carbondioxide, oxygen, or nitrogen. Some of the metals whose salts areespecially useful are silver, lead, mercury, and manganese. Useful saltsare combinations of these metals with organic saturated di-basic acidssuch as oxalic, malonic, succinic, glutaric and adipic acid, all ofwhich have less than 7 carbon atoms. Several tri-basic acids such ascitric acid, may also be used. Besides these groups of acid compounds, anumber of others are useful, such as silver formate, lead formate, leadthioacetate, and others.

We will now giveseveral embodiments of our; invention, which are givenbyway of example only.

Example I An emulsion is made up to contain two grams of silver oxalateper 100 c. c. in gelatin. This emulsion will contain This emulsion ismade by first adding the potassium oxalate to the gelatin solution andthen adding the silver nitrate with constant mechanical stirring. Afterthis gelatin-silver oxalate emulsion is prepared it is coated on asuitable support, chilled, dried, and preserved in the dark until readyfor-use. A very short exposure to ultra-violet light under a negative orpositive produces a latent image which is developed out upon heating theplate to approximately 100 C. for about 5 minutes. The intensity of theimage, of course, varies somewhat with the temperature and duration ofthe heat treatment. In this instance the image is a visible one.

Example II An emulsion is made up to contain two grams of mercurousoxalate in 100 c. c. in gelatin. This This emulsion is made by addingthe potassium oxalate solution to the gelatin solution and then addingthe mercurous nitrate solution with vigorous mechanical stirring. Theremainder of the treatment is thesame as that given under Example 1.

Example III suitable support and allowed to dry. After a short exposureto light a slightly visible image can be further developed out by heattreatment.

The general method of making these coating solutions is similar to thosegivenin the examples above. The metal salt is produced in the gelatinsolution by adding the required acid to another soluble salt of a metalin solution in the gelatin. In this manner the photothermographic saltwill remain in the layer either dissolved or suspended.

Among the carriers which may be used in this way are, besides gelatinand bakelite lacquer already mentioned, agar, casein, albumen, zein,drying oils, layers of regenerated cellulose, cellulose ethers, orcellulose esters, resins and siliceous enamel or glaze. In some casesthe carrier is chosen to suit the intensity of the subsequent heattreatment required. Some of the salts mentioned as suitable, forinstance, will require higher temperatures than others. Therefore, itwill be necessary to choose a carrier and support which will notdecompose nor be damaged by the treatment required. For example, gelatincoated on paper will be unsuited tothe process if the temperaturerequired will be as high as 150 C. or more, as the gelatin will tend todecompose and the paper will be damaged at temperatures much over this.Examples I and II will be satisfactory for use with gelatin on paper.

Our invention is useful either in the making of visible images, in themaking of relief images, or in certain planographic processes in whichan image differing from the background in surface texture will be ofadvantage. For obtaining a relief image, for example, it will bedesirable to use a colloid carrier which swells readily, such asgelatin, and a photothermographic salt, such as an oxalate, whichdecomposes into gaseous products at a relatively low temperature. If alayer containing these constituents is carefully heated the points atwhich the light has acted will swell into relief.

Under certain conditions an image can be obtained which differs from thebackground principally in that it has a different structure or surfacetexture. Thus in some cases it will be found after heating that theimage is distinguished from the background principally by having moregranularity, or being more porous. This property may be of use inproducing an ink or other transfer from such a surface to anothersupport.

The invention may also be useful in ceramic decoration. For such use acoating consisting of a suitable lacquer and a photothermographic saltyielding after high temperature treatment a suitable color will becoated upon porcelain, glass, or pottery, for example, and thensubjected to a high temperature to develop and burn it in. Thisapplication will, of course, be susceptible to wide variations.

Numerous other advantages and uses will be apparent.

We consider as included within our invention all variations andequivalents coming within the scope of the appended claims;

What we claim is:

1. The method of making a photographic image that comprises exposing toa light image a photosensitive layer comprising as its primaryconstituent a salt selected from the group consisting of the silver,lead, mercury, and manganous salts of organic saturated dibasic andtribasic acids,

silver formate, lead formate and lead thioacetate,

thereby forming a latent image therein and then submitting the layer toheat alone to develop a visible image therein.

2. The method of making a visible photo- ,graphic image that comprisesexposing to a light image a photosensitive layer comprising as itsprimary constituent an oxalate chosen from the following group, silveroxalate and mercurous oxalate, thereby forming a latent image, and thensubmitting the layer to heat alone to develop a visible image.-

3. The method of making a photographic image that comprises exposing toa light image a photosensitive layer comprising mercurous oxalate andthen heating the layer to develop an image therein.

4. The method of making a photographic image that comprises exposing toa light image a photosensitive layer comprising silver oxalate and thenheating the layer to develop an image therein.

5. A photothermographic element comprising a support and a sensitivecolloid layer thereon including as its primary photosensitiveconstituent a silver salt of an organic saturated dibasic acid of lessthan '7 carbon atoms, and free from added sensitizer.

6. A photothermographic element comprising a support and a. sensitivecolloid layer thereon including silver oxalate as its primaryphotosensitive constituent and free from added sensitizer.

'7. A photothermographic element comprising a support and sensitivecolloid layer thereon comprising as its primary constituent a saltselected from the group consisting of the silver, lead mercury andmanganous salts of organic saturated dibasic and tribasic acids, silverformate, lead formate and lead thioacetate and free from addedsensitizer.

,8. The method of making a photographic image that comprises exposing toa light image a photosensitive layer comprising as its primaryconstituent a heavy metal salt of an organic saturated dibasic acid ofless than seven carbon atoms and then heating the layer to develop animage therein.

9. A photothermographic element comprising a support, and a sensitivecolloid layer thereon including as its primary photosensitiveconstituent a heavy metal salt of an organic saturated dibasic acid ofless than '7 carbon atoms and free from added sensitizers.

10. A photothermographic element comprising a support and a sensitivecolloid layer thereon including as its primary photosensitiveconstituent an oxalate of a heavy metal and free from added sensitizer.

SAMUEL E. SHEPPARD.

WALDEMAR VANSELOW.

